Recently, the introduction of IRS in MIMO system to enhance the security has also made effective progress.
Dong et al. [1]} and Jiang et al. [2]} studied an IRS-aided secure MIMO communication system, where a base station (BS) equipped with multiple antennas communicates with a multi-antenna receiver in the presence of a multi-antenna Eve. Particularly, the joint design of the transmit covariance at the BS and the phase shift coefficients at the IRS was considered to maximize the SR. In [1]}, the barrier, Newton and backtracking line search methods were used to search for global optimal transmit covariance, while the MM algorithm was applied to obtain the local optimal phase shift coefficients. In [2]}, the successive convex approximation (SCA)-based algorithm was used to solve the optimization of the transmit covariance. For the design of the phase shift coefficients, the closed-form solution of each phase shift coefficient was individually provided in an alternating way while fixing other phase shift coefficients. Hong et al. [5]} considered an AN-aided secure MIMO communication system assisted by an IRS. With the aim for maximizing the SR, the BCD algorithm was exploited to alternately optimize the variables. Specifically, the optimal transmit covariance and AN covariance matrix were derived in semi-closed form by applying the Lagrangian multiplier method, and the optimal phase shifts were obtained in closed form by utilizing the MM algorithm. IRS-aided secure DM-MIMO system was studied in [6]}. Two confidential bit streams transmitted from Alice to Bob, different from the conventional DM where Alice only transmits single CBS to Bob. This paper demonstrated that the IRS significantly enhanced the SR of DM.
